1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to a plasma display panel and method for driving the same, which can increase discharge efficiency.
2. Background of the Related Art
A plasma display panel (hereinafter, referred to as “PDP”) displays images including characters or graphics since fluorescent material is emitted by ultraviolet rays of 147 nm occurring when inert mixed gases of He+Xe, Ne+Xe, He+Ne+Xe, etc. are discharged. It is easy for this PDP to be made thin and large. The PDP also provides an improved picture quality due to recent advanced technology. In particular, in a 3-electrode AC sheet discharge PDP, wall charges are accumulated on the surface of the PDP upon the discharge of the PDP and electrodes are protected from sputtering occurring due to the discharge. Therefore, the 3-electrode AC sheet discharge PDP advantageously has a low-voltage driving and a long life span.
FIG. 1 is a perspective view illustrating a discharge cell structure, which is arranged in an AC-type PDP in a matrix shape, and FIG. 2 is a plane view illustrating a discharge cell structure of a plasma display panel.
Referring to FIG. 1 and FIG. 2, the discharge cell of the 3-electrode AC sheet discharge type PDP includes a scan electrode Y and a sustain electrode Z formed on an upper substrate 10, and an address electrode X formed on a lower substrate 17. Each of the scan electrode Y and the sustain electrode Z includes transparent electrodes 12Y and 12Z, and metal bus electrodes 13Y and 13Z having a line width smaller than those of the transparent electrodes 12Y and 12Z and formed in an edge region of one side of the transparent electrodes.
The transparent electrodes 12Y and 12Z are usually formed of indium-tin-oxide (hereinafter, referred to as “ITO”) on the upper substrate 10. The metal bus electrodes 13Y and 13Z are formed on the transparent electrodes 12Y and 12Z usually using a metal such as chromium (Cr) and serve to reduce a voltage drop by the transparent electrodes 12Y and 12Z having a high resistance. An upper dielectric layer 14 and a protection film 16 are stacked on the upper substrate 10 in which the scan electrode Y and the sustain electrode Z are formed in parallel.
Wall charges occurred upon the plasma discharge is accumulated on the upper dielectric layer 14. The protection film 16 serves to prevent damage of the upper dielectric layer 14 due to sputtering generated upon the plasma discharge and to increase emission efficiency of secondary electrons. The protection film 16 is usually formed using magnesium oxide (MgO). A lower dielectric layer 22 and a diaphragm 24 are formed on the lower substrate 18 in which the address electrode X is formed. A fluorescent material layer 26 is covered on the lower dielectric layer 22 and the diaphragm 24.
The address electrode X is formed in the direction intersecting the scan electrode Y and the sustain electrode Z. The diaphragm 24 is formed in parallel to the address electrode X and serves to prevent ultraviolet rays and a visible ray generated due to the discharge from leaking toward neighboring discharge cells. The fluorescent material layer 26 is excited by ultraviolet rays generated upon the plasma discharge to generate a visible ray of one of red, green and blue. Inert mixed gases such as He+Xe, Ne+Xe and He+Ne+Xe for discharge are inserted into a discharge space of the discharge cell formed between the upper/lower substrates 10, 18 and the diaphragm 24.
In such a 3-electrode AC sheet discharge type PDP, one frame is driven with it divided into several sub-fields having different numbers of emission in order to implement the gray level of a picture. Each sub-field is divided into a reset period for generating discharge uniformly, an address period for selecting a discharge cell and a sustain period for implementing the gray scale depending on the number of discharge.
For example, if it is desired to display a picture using 256 gray scales as in FIG. 3, the frame period 16.67 ms corresponding to 1/60 second is divided into eight sub-fields SF1 to SF8. Furthermore, each of the eight sub-fields SF1 to SF8 is divided into a reset and address period and a sustain period. In the above, the reset and address period of each sub-field are same every sub-field, whereas the sustain period is increased in the ratio of 2n(n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field. As such, since the sustain period varies in each sub-field, it is possible to implement the gray scale of the picture.
FIG. 4 shows a waveform illustrating the driving method of a plasma display panel in the prior art.
Referring to FIG. 4, the sub-field SF included in one frame of the PDP is driven with it divided into a reset period RPD for initializing the whole screen, an address period APD for selecting a cell, and a sustain period SPD for maintaining discharge of a selected cell.
In the reset period RPD, the reset pulse (RP) is applied to the scan electrode Y. The reset pulse (RP) has a ramp waveform and has a shape in which the voltage is increased in a set-up period and the voltage is reduced in a set-down period. In the set-up period where the voltage is gradually increased, a plurality of fine set-up discharges are generated and wall charges are thus formed on the upper dielectric layer. Thereafter, in the set-down period where the voltage is gradually decreased, unnecessary charged particles are partially erased by a plurality of fine set-down discharges, whereby the wall charges are reduced to the extent that they help a next address discharge while not causing erroneous discharge. During the set-down period, a DC voltage of the positive polarity (+) is supplied to the sustain electrode Z. Regarding the DC voltage of the positive polarity (+), the scan electrode Y become a relative negative polarity (−) against the sustain electrode Z upon the set-down since the reset pulse is supplied in a gradually reducing manner. In other words, the wall charges generated upon the set-up are reduced since the polarity is reversed.
During the address period APD, the scan pulse SP of the negative polarity (−) is sequentially applied to the scan electrode Y and at the same time the data pulse DP of the positive polarity (+) is applied to the address electrode X. As the voltage difference between the scan pulse SP and the data pulse DP and the wall voltage generated in the reset period RPD are added, an address discharge is generated within a cell to which the data pulse DP is applied. Wall charges are generated within the cell selected by the address discharge.
In the sustain period SPD, sustain pulses SUSPy and SUSPz are alternately applied to the scan electrode Y and the sustain electrode Z. Then, in the cell selected by the address discharge, sustain discharge of a sheet discharge shape is generated between the scan electrode Y and the sustain electrode Z every time when every sustain pulses SUSPy and SUSPz are applied, while the wall voltage and the sustain pulses SUSPy and SUSPz within the cell are added thereto.
In the erase period EPD following the sustain period SPD, discharge is stopped, which is kept since the erase pulse EP is applied to the sustain electrode Z. The erase pulse EP has a ramp waveform so that the amount of emission is small or a short pulse width of about 1 μs for discharge erase. The charged particles are erased due the short erase discharge by the erase pulse EP, stopping the discharge.
FIG. 5a is a view illustrating a light-emitting region that is divided upon the sustain discharge and FIG. 5b is a graph showing voltage distribution depending on the light-emitting region shown in FIG. 5a. 
Referring to FIG. 5a and FIG. 5b, there is shown a divided region where an emission phenomenon occurs in a discharge space within a PDP cell upon the discharge. As shown in FIG. 5a, if a predetermined voltage is applied between the cathode (for example, the sustain electrode Z and the anode (for example, the scan electrode Y, discharge occurs between both the electrode due to emission of electrons. At this time, primary electrons emitted from the cathode are accelerated by an electric field applied between the two electrodes and thus collide with neutron particles, thus generating new electrons (i.e., secondary electrons).
The secondary electrons are strongly accelerated at a portion “A” in FIG. 5b where the amount of the electric field is relatively high as variation in the voltage is great. These secondary electrons continue to obtain energy while performing ionization, thereby reaching a region “B” in FIG. 5b. In the region “B” of FIG. 5b, the secondary electrons do not obtain energy any further and transfer neutron particles by collision. In this process, excited particles drop to the ground state to generate a visible ray and vacuum ultraviolet rays. This region is referred to as a negative glow region 2 as shown in FIG. 5a. 
Electrons, which passed through the negative glow region 2, have very weak energy to generally represent a uniform plasma state. This region is called a positive column region 4 as shown in FIG. 5a. In the positive column 4, only electrons having high energy in the entire not energy by an electric field excite gas to emit light. In this positive column 4, ionization is rarely generated but emission by excitation is generated a lot. It is thus known that energy is converted to light in total to produce a good efficiency.
In the conventional 3-electrode structure, however, it is impossible to form a wide positive column having good discharge efficiency because the distance between the scan electrode Y and the sustain electrode Z is narrow. Due to this, the conventional 3-electrode structure has a disadvantage that the discharge efficiency is low. Accordingly, there is a need for a structure in which a wide positive column can be formed.
Furthermore, a PDP, which is currently commercialized, has efficiency of 1˜1.5 lm/W. In some test sample level, efficiency of 2.0 lm/W has been reported. It can be said that such improvement in efficiency compared to the existing structure is caused due to the increase in the amount of Xe in a use gas from an adequate level to a high level 14% rather than structural improvement. In case of inert mixed gases such as Ne+Xe being currently used, the amount of Ne is about 95% and the amount of Xe is about 5%. Therefore, in order to increase discharge efficiency, the amount of Xe injected into the panel is raised to about 14%.
However, since the particle size of Xe is significantly larger than those of Ne, the path of charges is limited if the amount of Xe is high. Thus, a voltage for causing discharge must be increased. In other words, the increase in the amount of Xe results in increased breakdown and sustain voltage between the scan electrode Y and the sustain electrode Z. Furthermore, even in the driving, there occur a time delay in which discharge ignition is delayed due to an increased cooling effect of electrons by the application of a large amount of Xe, i.e., due to unsmooth migration of electrons as the particle size of Xe is significantly greater than that of Ne.
That is, the conventional PDP structure has a difficulty in increasing discharge efficiency without any problem such as time delay.